Optical fiber cables comprise optical fibers for transmission of optical signals and further comprise jacketing elements enclosing the optical fibers. For instance, buffer tubes surround a respective number of optical fibers, and the cable jacket surrounds a plurality of buffer tubes. The cable jacket and the buffer tubes are usually formed of synthetic materials.
For indoor applications, fire protection or at least fire resistance of optical fiber cables is vital, particularly since an optical fiber cable, once having caught fire, bears the risk of propagating the fire from one spot in a building to further rooms or areas. Accordingly, jacketing elements such as the cable jacket or the buffer tubes should be designed to be fire-resistant or even self-extinguishable.
One conventional way of designing the fire-resistant material of jacketing elements of optical fiber cables is to use an intumescent additive, that is a component that decomposes and/or reacts with the formation of a foam containing a gas, when subjected to heat in case of fire. Such intumescent agents are already known; in polymer-based sheathing materials of jacketing elements they produce a carbonaceous foam when ignited, thereby providing thermal protection of optical fibers, pushing back the fire front and spreading around the section of the fire cable exposed to the flames and/or heat. As long as the optical cable is surrounded by the carbonaceous foam and gas formation or foam formation is not yet exhausted, fire protection is maintained.
In case of fire, however, fire often produces high winds. Furthermore, water sprayed by the fire service or by water nozzles at the ceiling may wash away the protecting foam from the fiber cable, thus bearing the risk of re-ignition as long as the fire is not extinguished completely throughout the building. Furthermore, any contact of the heated cable with other objects or people may locally damage the foamed protection layer, thus again exposing the cable core.
It is the object of the present application to provide an optical fiber cable having improved fire resistance.